How to change default viewport shading in 2.8?
To change Default Studio lightning without using Matcaps/Shading modes:

Go to Edit > User Preferences > Lights and choose Edit Studio Lights.

Now you can change all 4 lights. Options are self-explanatory.

After making dreamed setup - Save as Studio Light and Save Preferences.

You can even download saved setup and share it.



Here is something similar to 2.79. Probably a bit to shiny: